Oh, Hyuk Jin (2008-08). Reburning renewable biomass for emissions control and ash deposition effects in power generation. Doctoral Dissertation. Thesis uri icon

abstract

  • Cattle biomass (CB) has been proposed as a renewable, supplementary fuel for co-firing and reburning. Reburning coal with CB has the potential to reduce NOx and Hg emissions from coal fired systems. The present research focuses on three areas of combustion: 1) Biomass reburning experiments are conducted to determine the optimum operating conditions for the NOx reduction using blends of coal and CB as reburn fuels. 2) Since CB contains higher ash contents compared to coals, the fouling behavior is also investigated under the transient and short-time operation. 3) Finally CB contains higher Cl compared to coals, which oxidizes Hg to HgCl2. To understand the Hg oxidation behavior, a fundamental study of Hg oxidation in coal combustion is conducted using a plug flow reactor (PFR). The main parameters investigated are types of the reburn fuel, reburn equivalence ratios (ERRBZ), O2 concentrations in the reburn gas, injection angles of the reburn fuel, cross-sectional geometries of the reburn nozzles, symmetric and asymmetric reburn injections, reburn heat inputs, baseline NOx concentrations, and presence and absence of the heat exchangers (HEX). The results of reburning show that CB is a very effective fuel in NOx reduction, and the extent of NOx reduction is strongly dependent to the ERRBZ. The optimum conditions of the boiler operation for biomass reburning are as follows: ERRBZ = 1.1, 45? upward circular reburn nozzles, 12.5% O2 in the reburn gas, symmetric injection, and presence of HEXs. To make an effective reburn process, the baseline NOx concentrations must be higher than 230 g/GJ (0.5 lb/mmBTU) and the reburn heat input higher than 20%. The results of ash fouling show the presence of ash in the hotter region of the furnace seems to promote heat radiation thus augmenting the heat transfer to the HEX. The growth of the layer of ash depositions over longer periods typically lowers overall heat transfer coefficients. The addition of HCl to Hg containing gases in the PFR significantly increases Hg oxidations. The addition of NO inhibited the overall reaction and shifted the reaction temperature higher while the addition of O2 promoted Hg oxidations and lowered the reaction temperature. For heterogeneous cases, the use of the VWT catalyst promotes the reduction of Hg0 and shifted the reaction temperatures lower than those for homogeneous cases.
  • Cattle biomass (CB) has been proposed as a renewable, supplementary fuel for co-firing and
    reburning. Reburning coal with CB has the potential to reduce NOx and Hg emissions from coal
    fired systems. The present research focuses on three areas of combustion: 1) Biomass reburning
    experiments are conducted to determine the optimum operating conditions for the NOx reduction
    using blends of coal and CB as reburn fuels. 2) Since CB contains higher ash contents compared
    to coals, the fouling behavior is also investigated under the transient and short-time operation. 3)
    Finally CB contains higher Cl compared to coals, which oxidizes Hg to HgCl2. To understand
    the Hg oxidation behavior, a fundamental study of Hg oxidation in coal combustion is conducted
    using a plug flow reactor (PFR).
    The main parameters investigated are types of the reburn fuel, reburn equivalence ratios
    (ERRBZ), O2 concentrations in the reburn gas, injection angles of the reburn fuel, cross-sectional
    geometries of the reburn nozzles, symmetric and asymmetric reburn injections, reburn heat
    inputs, baseline NOx concentrations, and presence and absence of the heat exchangers (HEX).
    The results of reburning show that CB is a very effective fuel in NOx reduction, and the extent of
    NOx reduction is strongly dependent to the ERRBZ. The optimum conditions of the boiler
    operation for biomass reburning are as follows: ERRBZ = 1.1, 45? upward circular reburn nozzles, 12.5% O2 in the reburn gas, symmetric injection, and presence of HEXs. To make an effective
    reburn process, the baseline NOx concentrations must be higher than 230 g/GJ (0.5 lb/mmBTU)
    and the reburn heat input higher than 20%.
    The results of ash fouling show the presence of ash in the hotter region of the furnace seems
    to promote heat radiation thus augmenting the heat transfer to the HEX. The growth of the layer
    of ash depositions over longer periods typically lowers overall heat transfer coefficients.
    The addition of HCl to Hg containing gases in the PFR significantly increases Hg oxidations.
    The addition of NO inhibited the overall reaction and shifted the reaction temperature higher
    while the addition of O2 promoted Hg oxidations and lowered the reaction temperature. For
    heterogeneous cases, the use of the VWT catalyst promotes the reduction of Hg0 and shifted the
    reaction temperatures lower than those for homogeneous cases.

publication date

  • August 2008